Superheater control



J1me 1952 J. MARSHALL SUPERHEATER CONTROL 2 SHEETS- SHEET 1 Filed May 29, 1946 INVENTOI? M 0Q. B):

June 17, 1952 J. MARSHALL 2,600,895

SUPERHEATER CONTROL Filed May 29, 1946 2 SHEETS-SHEE'I 2 2 h f 32 25 2a 28 a? 2 31 /9& Q

1\ CLOSED 7 48 ?k /9 Patented June 17, 1952 SUPERHEATER CONTROL Leonard J. Marshall, Tenafly, N. J., assigncr to Combustion Engineering-superheater, Inc., a

corporation of Delaware Application May 29, 1946, Serial No. 672,393

8 Claims. (Cl. 122479) This invention relates to superheaters and particularly to means for controlling superheated steam temperature.

Steam generating units operating at high pressures and steam temperatures are generally equipped with superheaters provided with means for maintaining steam temperatures at a substantially constant value for the upper range of the load. This control is usually effected either by dampers and by-passes that divert part of the flue gas away from the superheater range or by a desuperheater that reduces the temperature of the over-superheated steam to the desired value.

An object of this invention is to provide novel control means for varying the mean temperature difference between steam in the superheater tubes and the gases passing externally thereover.

Figure 1 is a diagrammatic illustration of one form of superheat control embodying the invention.

Figure 2 shows the valve illustrated in Fig. l adjusted to produce a difierent superheat.

Figure 3 illustrates another form of the invention.

As shown in Figure 1 the superheater comprises two sections l and II contacted successively by the hot products of combustion leaving the furnace I2. Bafiies l3 and I4 direct the flow of the products of combustion downwardly ever section I I. As disclosed herein the superheater sections are suspended in a steam boiler, of which only a fragment is shown in Fig. 1 including a steam drum l5 receiving the discharge of steam and water from boiler and water wall tubes |5 while the separated steam is conducted from steam drum 5 to dry drum via steam tubes It.

The steam from drum passes in two parallel paths through tubes l9 and 2|), the portion passing through tubes l9 being delivered to the intake header |9a of superheater section In and the part passing through tubes being delivered to a three-way valve 2|. The connections 22,23 and 24 to valve 2| are preferably placed '120 degs. apart and a rotatable gate in valve 2| which preferably covers approximately 120 degs. of the bore in valve 2| may be rotated from the position shown in Fig. 1 covering the connection 23 counterclockwise so as to cover connection 24, or it may be stopped in any intermediate position thereby covering any desired corresponding and supplementary proportions of connections 23 and 24. In this way gate 25 serves as a throttle controlling the amount of steam that flows to one of the connections 23 and 24 with a corresponding complementary amount flowing to the other. As

shown, the steam flow from drum it through tube 20 to connection 22 of valve 2|, thence through connection 24 of valve 2| and through tube 26 to the intake header 2? of superheater section I After flowing through superheater section II the steam discharges from outlet header 28 through tube 29 to the superheated steam offtake 30. A tube 38 joins connection 23 of valve 2| to the superheater steam offtake 30.

The steam which has passed through superheater section lt passes from its offtake header 3| through tube 32 into a second three-way valve 33 having connections 3 3, 35 and 36 and a valve gate 31 similar to that of valve 2|. In the position of valve gate 31 shown in Fig. 1 the steam from tube 32 passes through valve 33 via connections 35 and 3t and joins the steam from tube 29 to pass to the superheater ofitake 30. Thus, the steam flows in parallel through sections I!) and II of the superheater.

In Fig. 2 the valve gates 25 and 37 are in different positions. A portion of steam flows from drum II through tube Hi to the intake header |9a of superheater section i8 and from its ofitake header 3! via tube 32, valve 33 and tubes 39, 26, to the intake 27 of section After being partially superheated by flowing through section I, the steam leaves by way of outlet header 28, flows through conduit 29 and enters superheated steam offtake 3B. Thus, as described, some of the steam flows serially through sections it and H of the superheater. Another portion of the steam flows from drum it via tube 2% through valve 2| and pipe 38 directly to superheater offtake 33.

In operating with the valves 2|, 33 set as in Fig. l, a portion of the saturated steam from drum I! flows through section iii of the superheater for any rate of evaporation. At low ratings (below those for which the final temperature of the steam is controlled) the remaining portion of the saturated steam in parallel passes through section I At the higher ratings where the temperature of the steam is to be controlled, valve gate 25 of valve 2| may be set to cover portions of both connections 23 and 2 3 thereby causing the portion of saturated steam passin through valve 2| to be apportioned between superheater section H and the superheater offtake 39.; for maximum control, the valve gate 25, as shown in Fig. 2, covers connection 2t and causes all of said portion of saturated steam to be diverted through tube 25, valve 2| and tube 38- directly to the ofitake 39. The controllable flow resistance of this path, through tube 26, valve 2| and tube 38, precludes an excess of steam through Tube 43 also connects to a valve 55.

this circuit. The remaining steam flows from drum l1 through pipe I9 to superheater section to and serially through section II; its amount depends upon the resistance of the circuit through tube 20, valve 2| and tube 38.

Intermediate positions of valve gate 3! of valve 33 between those shown in Figs. 1 and ,2 cause a portion of the steam from section E9 to flow to the offtake 30 and the remaining portion to join saturated steam from valve 2| going to sec tion H. Obviously the valves 2i and 23 may be mechanically interconnected to be operated together, as indicated at 41, 48 in Fig. 2.

In the valve setting where steam passesserially through superheater sections l and H the highly superheated steam leaving said sections mixes with the saturated steam through the lay-pass formed by tubes and 38 and the temperature of the mixture is considerably below that which occurs when all of the steam flows in parallel through said sections. This reduction in steam temperature is the result of a-reduced mean temperature difference between the gases surrounding section I l and the steam in section H of the superheater. Calculations indicate that with assumed conditions of 1900 degs. F. gas temperature when first contacting the superheater and 1000 degs. F. steamtemperature, this method of control will give a reduction in the steam temperature of 140 degs. F. over what would result from directing all the steam through sections I ii, I I in parallel. For this amount of control, additional alloy tubing would be required in thesuperheater.

However, the'maximum reduction in steam temperature generally required is approximately as from'tube 32 through check valve to the intake header 2'! of superheater section I'l via tube 25. Another tube 6 connects drum H to valve 45. Valves 42 and 45 may be interconnected by connectin rod 41 and levers 48 so as to operate together. 'In this arrangement superheated steam from sec tion It may be mixed with saturated steam and the mixture may be passed through section .I I of the superheater. When not operating to control steam temperature, the valves 42 and "65 are in open position and the saturated steam flows in parallel through sections [8 and H of the superheater. For extreme control the valves 52 and 45 are moved to closed position and the steam flows through sections it! and II serially. For intermediate control of steam temperature valves 42 and 4,5 are partially closed to cause superheated steam to flow from the outlet of section In, through valve 44 and mix with saturated steam flowing through valve 45, the mixture then flowing through section H of the superheater. The advantage of the embodiment illustrated in Fig. 3 lies in an increased steam flow through both sections l0 and H of the superheater because at no time will saturated steam by-pass the superheater heating surface sections ll) and H mentioned above in the way provided for in Figs. 1 and 2 through pipe line 20, valve 2! and pipe line 38. This increased steam flow (through both superheater sections [9 and It) for a given heat second section exposed to a medium flowing serially over the first and second sections for heatingsaidfluid; a source of fluid and a heated fluid offtake; means conducting a part of said fluid to said first section to be heated therein; means conducting heated fluid from said first section selectively either to said ofitake or to the inlet of said second section, or proportionately to both; means conducting the remainder of said fluid from said source selectively either to the inlet of said second section or to said heated fluid offtake, or proportionately to both.

2. In a heater for heating fluid from a fluid source and comprising a first and second section exposed to a-heating medium flowing serially over the first and second sections for heating said fluid; a conduit conveying a part of said fluid to said first section; a conduit conveying heated fluid from said first section; a three-way valvehaving three ports, a first port being connected to said last conduit; a fluid offtakeconnected to asecond port of said valve; a second three-way valve having three ports; a conduit conveying the remainder of said fluid from said source to a first port of said second three-way valve; conduits connecting a second port of said second valve to a'third port of said first'valve and to the inlet'of said second section a conduit connecting the outlet of said second section to said offtake for heated fluid; a conduit connecting a third port of said second valve to said offtake; and means in said valve to controllably close off one, or simultaneously, portions of both of said second and third ports in each valve.

3. In a superheater comprising first and second heat exchange sections exposed to a heating medium flowing serially over said sections, a supply of saturated steam, and an ofitalre for superheated steam; a conduit conveying a part of said saturated steam to said first section; a second conduit conveying partially superheated steam from said first section to said offtake; a valve connected into said second conduit; a third conduit conveying the remainder of said saturated steam to a second valve; a fourth conduit connecting said second valve to said second conduit between the first valve and the first section; a branch conduit connecting said fourth conduit to the inlet of said second section; a check valve in said fourth conduit between said second and branch conduits to prevent flow from said second conduit to said branch conduit; and a connection between the outlet of said second section and said ofi'take.

4. In a fluid heater comprising a first heat exchanger section exposed to a hot heating medium and a second heat exchanger section exposed to a relatively cooler heating medium; a source of fluid to be heated and a heated fluid ofitake; means conducting a portion of said fluid to and through said first section and thence in part or in whole through either said second section to said offtake or directly to said offtake; means controllably conducting a second part of said fluid in part or in whole to join the heated first portion to said second section and therethrough to said ofitake, or directly to said offtake.

5. In a superheater comprising first and second heat exchange sections exposed to a heating medium flowing serially over said sections, a source of saturated steam, and an offtake for superheated steam; a first inlet conduit connecting said source with the inlet of said first section and a second inlet conduit connecting said source with the inlet of said second section; a first outlet conduit connecting the outlet of said first section with the inlet of said second section; a second outlet conduit connecting the outlet of said second section to said offtake; a

passageway connecting the outlet of said first section with said ofitake; first valve means associated with said passageway operable to proportionally distribute the steam, flowing from said first section, between said offtake and the inlet of said second section; second valve means associated with said second inlet conduit to control the volume of saturated steam flowing to said second section; and a check valve in the first outlet conduit and remote from said passageway, arranged to prevent flow from the inlet of said second section to the outlet of said first section.

6. In a superheater comprising first and second heat exchange sections exposed to a heating medium flowing serially over said sections, a supply of saturated steam, and an offtake for superheated steam; a first conduit connecting the inlet of said first superheater section with said supply source; a second conduit connecting the inlet of said second superheater section with said supply source; a third conduit connecting the outlet of said first section with the inlet of said second section; a fourth conduit connecting the outlet of said second section to said offtake; a fifth conduit connecting the outlet of said first superheater section with said offtake; valve means associated with said fifth conduit at a location to control fiow directly to said ofitake; and other valve means associated with said second conduit at a location to control flow from said saturated steam source.

7. In a superheater comprising first and second heat exchange sections exposed to a heating medium flowing serially over said sections, a source of saturated steam and an offtake for superheated steam; a first inlet conduit con- 4 necting said source with the inlet of said first section and a second inlet conduit connecting said source with the inlet of said second section;

a first outlet conduit connecting the outlet of said first section with the inlet of said second section; a second outlet conduit connecting the outlet of said second section to said offtake; a passageway between the outlet of said first superheater section and said ofitake; a by-pass conduit between the source of saturated steam and said superheated steam oil'take; first valve means associated with both said passageway and also with said first outlet conduit; apparatus for actuating said first valve means to proportionally distribute the steam, flowing from said first section, between said offtake and said second section inlet; second valve means associated with both said by-pass conduit and said second inlet conduit; and apparatus for actuating said sec= ond valve means for distributing saturated steam between said second section and said ofiftake.

8. In a superheater comprising first and sec ond heat exchange sections exposed to a heating medium flowing serially over said sections; a source of saturated steam and an offtake for superheated steam; a first inlet conduit c0nnect ing said source with the inlet of said first section, and a second inlet conduit connecting said source with the inlet of said second section; a first outlet conduit connecting the outlet of said first section with the inlet of said second section, and a second outlet conduit connecting the outlet of said second section with said offtake; a passageway between said first outlet conduit and said ofl'take; valve means associated with both, said passageway and said first outlet conduit; apparatus for actuating said valve means to proportionally distribute the steam flowing from said first section, between said passage= way leading to said offtake and said first outlet conduit leading to the inlet of said second section; other valve means in said second inlet conduit, said other valve means communicating directly with said superheated steam oiftake; and apparatus for actuating said other valve means to proportion the volume of saturated steam between said second section and said ofitake.

LEONARD J. MARSHALL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,073,305 Thomsen et al Sept. 16, 1913 1,973,517 Armacost Sept. 11, 1934 2,061,363 Lucke Nov. 17, 1936 2,087,972 Heller July 27, 193 2,463,888 Linaker Mar. 8, 1949 

